Random access preamble design

ABSTRACT

A communication method performed by a base station in a wireless communication network is disclosed. The base station notifies a terminal of a cyclic shift increment NCS configuration information indicating an NCS value. The base station then receives from the terminal a random access preamble related to the NCS value indicated by the NCS configuration information. The NCS value belongs to a set of cyclic shift increments including all of the following cyclic shift increments of 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/878,455, filed on May 19, 2020, which is a continuation of U.S.patent application Ser. No. 16/378,096, filed on Apr. 8, 2019, now U.S.patent Ser. No. 10/708,817, which is a continuation of U.S. patentapplication Ser. No. 14/557,088, filed on Dec. 1, 2014, now U.S. Pat.No. 10,285,092, which is a continuation of U.S. patent application Ser.No. 14/045,554, filed on Oct. 3, 2013, now U.S. Pat. No. 8,913,696. TheU.S. patent application Ser. No. 14/045,554 is a continuation of U.S.patent application Ser. No. 12/605,616, filed on Oct. 26, 2009, now U.S.Pat. No. 8,599,974. The U.S. patent application Ser. No. 12/605,616 is acontinuation of International Patent Application No. PCT/CN2008/070768,filed on Apr. 22, 2008, which claims priority to Chinese PatentApplication No. 200710074200.1, filed on Apr. 30, 2007. All of theafore-mentioned patent applications are hereby incorporated by referencein their entireties.

TECHNICAL FIELD

The disclosure relates to the technology of mobile communication, andmore particularly, to the design of a Random Access Preamble (RAP).

BACKGROUND

In a mobile communication system, a Random Access Preamble is normallytransmitted to a base station by a mobile terminal to initiate therandom access procedure and to enable synchronization of the mobileterminal with the base station.

There are 64 preambles in each cell in the document of “3GPP TS36.211v1.0.0—Physical Channels and Modulation” which was published in March2007. When initiating a random access procedure, a mobile terminaltransmits one of the 64 preambles. A message is transmitted to a basestation by the mobile terminal selecting a particular preamble.

Before transmitting the preamble, a mobile terminal must synchronize tothe carrier frequency and the frame timing of a base station to becomedownlink synchronized. Although the mobile terminal is downlinksynchronized, there is uncertainty when a signal transmitted by themobile terminal arrives at the base station. This is because a mobileterminal far away from the base station will receive downlink signalswith a larger delay than a mobile terminal close to the base station,and the transmitted signals in uplink will take longer time to propagateto the base station for a mobile terminal which is far away from thebase station compared to the signals from a mobile terminal close to thebase station. The uncertainty in round trip time causes interferencesbetween uplink signals transmitted by different mobile terminals unlessuplink synchronization is performed before data transmission in uplink.

The transmission of any of the RAPs allows a base station to estimatethe time of arrival of an uplink signal. The base station can then,based on the time of arrival estimate, transmit a time advance commandto a mobile terminal to ensure uplink synchronization. Hence, once apreamble is transmitted by a mobile terminal, the base station maydetect which preamble has been transmitted and estimate the time ofarrival.

To obtain good detection properties of the preambles, or to accuratelyestimate the time of arrival of the uplink signal, the set of preamblesshould be designed to have good autocorrelation and cross-correlationproperties.

The set of RAPs in Evolved UTRA (E-UTRA) is defined from one or severalroot sequences. A subset of the preambles x_(u,v)(k) is generated fromthe u^(th) order root Zadoff-Chu (ZC) sequence x_(u)(k) by cyclic shiftsof a plurality of the shift increments N_(CS). Specifically, x_(u,v)(k)may be generated according to the equation below:x _(u,v)(k)=x _(u,v)((k+

N _(CS))mod N _(ZC)),  (1)where v is an integer, and N_(ZC) is the length of the ZC sequencedefined by:x _(u)(k)=W ^(uk(k+1)/2) ,k=0,1, . . . ,N _(ZC)−1,W=e ^(−j2π/N) ^(ZC),j=√{square root over (−1)}  (2)

The number of preambles that may be generated from a single rootsequence is N_(pre)=

N_(ZC)/N_(CS)

, where

n

denotes the largest integer not greater than n. If N_(pre)<64, thenseveral preamble subsets generated from different root sequences arerequired to obtain 64 preambles in a cell. The cross-correlation betweendifferent root sequences is small but still larger than thecross-correlation between sequences generated by a single root sequence.Thus it is beneficial for the detection performance to have N_(pre)=64if N_(pre) could not be set greater.

The number of ZC sequences contained in each set of ZC sequences withlength of N_(ZC) is N_(ZC)−1. If the number of root sequences forobtaining the 64 preambles of a cell is N_(r), N_(r)=

64/Npre

, where

n

denotes the minimal integer not smaller than n, then the number ofdisjoint sets is N_(D)=

(N_(ZC)−1)/N_(r)

. Different cells in a network should make use of preambles obtainedfrom disjoint sets of root sequences, so that the base station knowswhether a transmitted preamble is intended for a certain cell or not.The larger the number of root sequences N_(r) that is needed forobtaining 64 preambles in a cell, the smaller is the number of disjointsets of RAPs N_(D). Thus, from network planning perspective, it isdesirable to have N_(pre)=64, and if that is not possible, to have ashigh value as possible of N_(pre).

A subset of preambles generated with equation (1) is a set of so-calledZero-Correlation Zone (ZCZ) sequences. The definition for a set of ZCZsequences is as follows: a set of M sequences {d_(v)(k)},

=0, 1, . . . , M−1, k=0, 1, . . . , N−1, of length N, is said to be aset of ZCZ sequences, if all the sequences in the set satisfy thefollowing autocorrelation and cross-correlation properties:

The periodic autocorrelation function

$\sum\limits_{k = 0}^{N - 1}{{d_{v}(k)}{d_{v}^{*}\left( {\left( {k + p} \right){mod}N} \right)}}$is zero for all p such that 0<|p|≤T, and the periodic cross-correlationfunction

$\sum\limits_{k = 0}^{N - 1}{{d_{v}(k)}{d_{w}^{*}\left( {\left( {k + p} \right){mod}N} \right)}}$is zero for all p such that |p|≤T (including p=0), where T is the lengthof the ZCZ.

A ZC sequence has ideal periodic autocorrelation, for example,

$\sum\limits_{k = 0}^{N - 1}{{x_{u}(k)}{x_{u}^{*}\left( {\left( {k + p} \right){mod}N} \right)}}$is zero for all nonzero p. Thus the set of preambles defined as cyclicshifts of the root sequence according to equation (1) is a set of ZCZsequences, where the ZCZ length is T=N_(CS)−1.

Based on N_(pre)=

N_(ZC)/N_(CS)

, N_(CS) should be as small as possible in order to make N_(pre) be asgreat as possible. But the value of N_(CS) should not be too small. In abase station a bank of correlators are used when receiving RAPs, so thatthere is one correlator for each preamble. Each correlator outputs timeof arrival from 0 to T×T_(s)=(N_(CS)−1)×T_(s), where T_(s) is the symbolperiod of the sequence. The ZCZ property of the set of preambles impliesthat the correlator for any preamble will give a zero output if anyother preamble is transmitted as long as the sum of the round trip timeand delay spread in the cell is less than or equal to the product of thelength of ZCZ and T_(s) (i.e., T×T_(s)). The maximum round trip timeT_(r) in a cell is given by the cell radius R: T_(r)=2R/c, where c isthe speed of light. Thus, the minimum value of the length of ZCZ and theminimum value of N_(CS) length for a certain cell increase with the cellradius. Therefore, the value of the selected N_(CS) should be largeenough to ensure that the conditions mentioned above are satisfied.

Since the cell radius to be supported in E-UTRA is from 1 km to 100 km,and since N_(CS) should be as small as possible for any given cell,there is a need for multiple values of N_(CS). The value of an N_(CS) ina cell is broadcast to a mobile terminal by a base station. Of course,the base station may broadcast the length of ZCZ to the mobile terminal,so that the mobile terminal knows how to generate preambles. It isdesirable to have as small amount of signaling as possible on thebroadcast channel to save overload. Therefore, to achieve low signalingoverload, there should be a limited predefined set of values of N_(CS)or a set of lengths of ZCZ.

Currently, it is proposed in the 3GPP Tdoc “R1-071661-On constructionand signaling of RACH preambles” disclosed in March 2007 that, thecyclic shift increment value N_(CS) in the cell was proposed to besignalled to the UE but there was no restriction on the values of thecyclic shift increment, which would then give a substantial amount ofsignalling. An alternative proposal is given in the 3GPP Tdoc“R1-071471—Outstanding issues in random access preamble design forE-UTRA” disclosed in March 2007, which is to have 11 values of N_(CS)without specification how to select the values. Of course, it is notdescribed in these documents how to select the lengths of ZCZ either.Currently there is no feasible scheme for selecting an appropriatelimited set of ZCZ lengths, in order to ensure a small and limitedsignaling overload.

SUMMARY

According to a first aspect of the disclosure, a method of facilitatinga user equipment (UE) communicating with a base station (BS) via a cellof a mobile communications system is provided. The UE selects a randomaccess preamble (RAP) from a set of RAPs, and transmits the RAP to theBS. The BS receives the RAP, and estimates a time of arrival of the RAP.The set of RAPs is included in 64 RAPs available in the cell. The 64RAPs are obtained from at least one Zadoff-Chu sequence. The at leastone Zadoff-Chu sequence is used in generation of RAP sequencesx_(u,v)(k) for the 64 RAPs. x_(u,v)(k) is given by:x_(u,v)(k)=x_(u,v)((k+

N_(CS)) mod N_(ZC)), where u and v are integers, N_(ZC) is a length ofthe at least one Zadoff-Chu sequence, N_(CS) is given by a pre-definedset including all of the following values: 0, 13, 15, 18, 22, 26, 32,38, 46, 59, 76, 93, 119, 167, 279, 419. And Zadoff-Chu sequence isdefined by: x_(u)(k)=W^(uk(k+1)/2), k=0, 1, . . . , N_(ZC)−1,W=e^(−j2πN) ^(ZC) , j=√{square root over (−1)}.

According to a second aspect of the disclosure, a mobile communicationssystem is provided. The system includes a UE in communication with a BSvia a cell of the system. The UE is configured to select a RAP from aset of RAPs, and transmit the RAP to the BS. The BS is configured toreceive the RAP, and estimate a time of arrival of the RAP. The set ofRAPs is included in 64 RAPs available in the cell. The 64 RAPs areobtained from at least one Zadoff-Chu sequence. The at least oneZadoff-Chu sequence is used in generation of RAP sequences x_(u,v)(k)for the 64 RAPs. x_(u,v)(k) is given by:x _(u,v)(k)=x _(u,v)((k+

N _(CS))mod N _(ZC)),where u and v are integers, N_(ZC) is a length of the at least oneZadoff-Chu sequence, N_(CS) is given by a pre-defined set including allof the following values: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93,119, 167, 279, 419. And Zadoff-Chu sequence is defined by:x _(u)(k)=W ^(uk(k+1)/2) ,k=0,1, . . . ,N _(ZC)−1,W=e ^(−j2π/N) ^(ZC),j=√{square root over (−1)}.

According to a third aspect of the disclosure, a UE is provided. The UEincludes a memory retaining instructions and a processor coupled to thememory. The processor is configured to execute the instructions retainedin the memory. The instructions relate to the UE selecting an RAP from aset of RAPs, and the UE transmitting the RAP to a BS. The UE is capableof communicating with the BS via a cell of a mobile communicationssystem. The set of RAPs is included in 64 RAPs available in the cell.The 64 RAPs are obtained from at least one Zadoff-Chu sequence. The atleast one Zadoff-Chu sequence is used in generation of RAP sequencesxu,v(k) for the 64 RAPs. xu,v(k) is given by:x _(u,v)(k)=x _(u,v)((k+

N _(CS))mod N _(ZC)),where u and v are integers, N_(ZC) is a length of the at least oneZadoff-Chu sequence, N_(CS) is given by a pre-defined set including allof the following values: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93,119, 167, 279, 419. And Zadoff-Chu sequence is defined by:x _(u)(k)=W ^(uk(k+1)/2) ,k=0,1, . . . ,N _(ZC)−1,W=e ^(−j2π/N) ^(ZC),j=√{square root over (−1)}.

According to a fourth aspect of the disclosure, a BS is provided. The BSincludes a memory retaining instructions and a processor coupled to thememory. The processor is configured to execute the instructions retainedin the memory. The instructions relate to the BS receiving an RAP andestimating a time of arrival of the RAP. The RAP is selected from a setof RAPs. The BS is capable of communicating with a UE via a cell of amobile communications system. The set of RAPs is included in 64 RAPsavailable in the cell. The 64 RAPs are obtained from at least oneZadoff-Chu sequence. The at least one Zadoff-Chu sequence is used ingeneration of RAP sequences x_(u,v)(k) for the 64 RAPs. x_(u,v)(k) isgiven by: x_(u,v)(k)=x_(u,v)((k+

N_(CS)) mod N_(ZC)), where u and v are integers, N_(ZC) is a length ofthe at least one Zadoff-Chu sequence, N_(CS) is given by a pre-definedset including all of the following values: 0, 13, 15, 18, 22, 26, 32,38, 46, 59, 76, 93, 119, 167, 279, 419. And Zadoff-Chu sequence isdefined by:x _(u)(k)=W ^(uk(k+1)/2) ,k=0,1, . . . ,N _(ZC)−1,W=e ^(−j2π/N) ^(ZC),j=√{square root over (−1)}.

In addition, the disclosure provides a communication method, comprising:notifying, by a base station in a wireless communication network, aterminal of a cyclic shift increment configuration informationindicating a cyclic shift increment value N_(CS) (N_(CS) value), theN_(CS) value belonging to a set of cyclic shift increments includingnon-zero cyclic shift increments N_(CS)(k); and receiving, by the basestation from the terminal, a random access preamble related to theN_(CS) value indicated by the cyclic shift increment configurationinformation; and wherein N_(CS)(k) satisfies following formula:N _(CS)(k)=

N _(ZC) /[N _(pre)(0)×a ^(k) +a/(1−a)×(a ^(k)−1)]

,k=0,1,2 . . . K;

wherein

N_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)]

denotes a maximum integer not greater thanN_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)],[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)] denotes a nearest integer toN_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1), N_(pre)(0)=64, N_(zc) denotes alength of a Zadoff-Chu sequence corresponding to the random accesspreamble, and K=14; and wherein a=0.856 or a satisfies followingformula:

$2 = {{64 \times a^{14}} + {\frac{a}{1 - a}{\left( {a^{14} - 1} \right).}}}$

As a possibility, the set of cyclic shift increments further includes avalue 0, and the N_(CS) value of 0 in the set of cyclic shift incrementsindicates that one preamble sequence is generated from one rootsequence.

As a possibility, the random access preamble belongs to a set of randomaccess preambles.

As a possibility, the set of random access preambles is derived from atleast one Zadoff-Chu sequence.

As a possibility, the at least one Zadoff-Chu sequence is used ingeneration of a sequence xu,v(k) for the set of random access preambles,and the sequence xu,v(k) is given by:

x_(u,v)(k)=x_(u)((k+vN_(CS)) mod N_(ZC)), where u and v are integers,N_(ZC) is a length of the at least one Zadoff-Chu sequence,x_(u)(k)=e^(−jπuk(k+1)/N) ^(ZC) , k=0, 1, . . . , N_(ZC)−1, andj=√{square root over (−1)}.

As a possibility, random access preambles derived from a same Zadoff-Chusequence in the set of random access preambles have zero correlationzones of a length N_(CS)−1.

As a possibility, the set of random access preambles comprises 64 randomaccess preambles.

Moreover, the disclosure provides a base station operable to communicatein a wireless communications network, the base station comprising: aprocessor; and a non-transitory computer readable storage medium storingprogramming for execution by the processor coupled to the storagemedium, the programming including instructions that direct the basestation to: notify a terminal of a cyclic shift increment configurationinformation indicating a cyclic shift increment value N_(CS) (N_(CS)value), the N_(CS) value belonging to a set of cyclic shift incrementsincluding non-zero cyclic shift increments N_(CS)(k); and receive, fromthe terminal, a random access preamble related to the N_(CS) valueindicated by the cyclic shift increment configuration information; andwherein N_(CS)(k) satisfies following formula:N _(CS)(k)=

N _(ZC) /[N _(pre)(0)×a ^(k) +a/(1−a)×(a ^(k)−1)]

,k=0,1,2 . . . K;

wherein

N_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)]

denotes a maximum integer not greater thanN_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)],[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)] denotes a nearest integer toN_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1), N_(zc) denotes a length of aZadoff-Chu sequence corresponding to the random access preamble, andK=14; and wherein a=0.856 or a satisfies following formula:

$2 = {{64 \times a^{14}} + {\frac{a}{1 - a}{\left( {a^{14} - 1} \right).}}}$

As a possibility, the set of cyclic shift increments further includes avalue 0, and the NCS value of 0 in the set of cyclic shift incrementsindicates that one preamble sequence is generated from one rootsequence.

As a possibility, the random access preamble belongs to a set of randomaccess preambles.

As a possibility, the set of random access preambles is derived from atleast one Zadoff-Chu sequence.

As a possibility, the at least one Zadoff-Chu sequence is used ingeneration of a sequence xu,v(k) for the set of random access preambles,and the sequence xu,v(k) is given by:

x_(u,v)(k)=x_(u)((k+vN_(CS)) mod N_(ZC)), where u and v are integers,N_(ZC) is a length of the at least one Zadoff-Chu sequence,x_(u)(k)=e^(−jπuk(k+1)/N) ^(ZC) , k=0, 1, . . . , N_(ZC)−1, andj=√{square root over (−1)}.

As a possibility, random access preambles derived from a same Zadoff-Chusequence in the set of random access preambles have zero correlationzones of a length NCS−1.

As a possibility, the set of random access preambles comprises 64 randomaccess preambles.

Further, the disclosure provides a communication method, comprising:receiving, by a terminal apparatus in a wireless communication networkfrom a base station, a cyclic shift increment configuration informationindicating a cyclic shift increment value NCS (NCS value), the NCS valuebelonging to a set of cyclic shift increments including non-zero cyclicshift increments N_(CS)(k); and sending, by the terminal apparatus tothe base station, a random access preamble related to the NCS valueindicated by the cyclic shift increment configuration information; andwherein N_(CS)(k) satisfies following formula:N _(CS)(k)=

N _(ZC) /[N _(pre)(0)×a ^(k) +a/(1−a)×(a ^(k)−1)]

,k=0,1,2 . . . K;

wherein

N_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)]

denotes a maximum integer not greater thanN_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)],[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)] denotes a nearest integer toN_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1), N_(pre)(0)=64, N_(zc) denotes alength of a Zadoff-Chu sequence corresponding to the random accesspreamble, and K=14; and wherein a=0.856 or a satisfies followingformula:

$2 = {{64 \times a^{14}} + {\frac{a}{1 - a}{\left( {a^{14} - 1} \right).}}}$

As a possibility, the set of cyclic shift increments further includes avalue 0, and the N_(CS) value of 0 in the set of cyclic shift incrementsindicates that one preamble sequence is generated from one rootsequence.

As a possibility, the random access preamble belongs to a set of randomaccess preambles.

As a possibility, the set of random access preambles is derived from atleast one Zadoff-Chu sequence.

As a possibility, the at least one Zadoff-Chu sequence is used ingeneration of a sequence xu,v(k) for the set of random access preambles,and the sequence xu,v(k) is given by:

xu,v(k)=xu((k+vNCS) mod NZC), where u and v are integers, NZC is alength of the at least one Zadoff-Chu sequence, xu(k)=e^(−jπuk(k+1)/N)^(ZC) , k=0, 1, . . . , NZC−1, and j=√{square root over (−1)}.

As a possibility, random access preambles derived from a same Zadoff-Chusequence in the set of random access preambles have zero correlationzones of a length NCS−1.

As a possibility, the set of random access preambles comprises 64 randomaccess preambles.

Further, the disclosure provides a terminal apparatus, comprising: aprocessor; and a non-transitory computer readable storage medium storingprogramming for execution by the processor coupled to the storagemedium, the programming including instructions that direct the terminalapparatus to: receive, from a base station, a cyclic shift incrementconfiguration information indicating a cyclic shift increment valueN_(CS) (N_(CS) value), the N_(CS) value belonging to a set of cyclicshift increments including non-zero cyclic shift increments N_(CS)(k);and send, to the base station, a random access preamble related to theN_(CS) value indicated by the cyclic shift increment configurationinformation; and wherein N_(CS)(k) satisfies following formula:N _(CS)(k)=

N _(ZC) /[N _(pre)(0)×a ^(k) +a/(1−a)×(a ^(k)−1)]

,k=0,1,2 . . . K;

wherein

N_(ZC)/N_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)]

denotes a maximum integer not greater thanN_(ZC)/[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)],[N_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1)] denotes a nearest integer toN_(pre)(0)×a^(k)+a/(1−a)×(a^(k)−1), N_(pre)(0)=64, N_(zc) denotes alength of a Zadoff-Chu sequence corresponding to the random accesspreamble, and K=14; and wherein a=0.856 or a satisfies followingformula:

$2 = {{64 \times a^{14}} + {\frac{a}{1 - a}{\left( {a^{14} - 1} \right).}}}$

As a possibility, the set of cyclic shift increments further includesvalue 0, and the NCS value of 0 in the set of cyclic shift incrementsindicates that one preamble sequence is generated from one rootsequence.

As a possibility, the random access preamble belongs to a set of randomaccess preambles.

As a possibility, the set of random access preambles is derived from atleast one Zadoff-Chu sequence.

As a possibility, the at least one Zadoff-Chu sequence is used ingeneration of a sequence xu,v(k) for the set of random access preambles,and the sequence xu,v(k) is given by:

xu,v(k)=xu((k+vNCS) mod NZC), where u and v are integers, NZC is alength of the at least one Zadoff-Chu sequence, xu(k)=e^(−jπuk(k+1)/N)^(ZC) , k=0, 1, . . . , NZC−1, and j=√{square root over (−1)}.

As a possibility, random access preambles derived from a same Zadoff-Chusequence in the set of random access preambles have zero correlationzones of a length NCS−1.

As a possibility, the set of random access preambles comprises 64 randomaccess preambles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating an method embodiment of thedisclosure;

FIG. 2 is a diagram illustrating the relationship between the maximumnumber of preambles and the cell radius according to an embodiment ofthe disclosure;

FIG. 3 is a diagram illustrating the value of maximum relativedifference in the cell radius interval k according to an embodiment ofthe disclosure;

FIG. 4 is a block diagram of the base station according to an embodimentof the disclosure; and

FIG. 5 is a diagram illustrating the mobile communication systemaccording to an embodiment of the disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The general solution of an embodiment of the disclosure is describedfirst, incorporating FIG. 1 . As illustrated in FIG. 1 , the embodimentincludes:

Step 101: The length of the root sequence is determined.

Step 102: A set of ZCZ lengths is selected so that, for any cell radius,the maximum number of preambles determined from a ZCZ length which isselected from the selected set of ZCZ lengths, and is applicable to thecell and capable of determining a maximum number of preambles, isclosest to the maximum number of preambles obtained from a ZCZ lengthwhich is selected from the set of all integers, and is applicable to thecell and capable of determining a maximum number of preambles, whereinthe maximum number of preambles is determined from the length of theroot sequence and a ZCZ length selected.

In an embodiment of the disclosure, it should be ensured that theproduct of a ZCZ length and the symbol period of the sequence is greaterthan the sum of the round trip time and the delay spread of a cell,i.e., T×T_(s)>T_(r)+T_(d), in which, T is the length of ZCZ, T_(s) isthe symbol period, T_(r) is the round trip time, and T_(d) is the delayspread.

Since the maximum round trip time T_(r) in a cell is determined by thecell radius R, i.e., T_(r)=2R/c, where c is the speed of light,T×T_(s)>T_(r)+T_(d) may be rewritten as T×T_(s)>2R/c+T_(d).

Furthermore, since T=N_(CS)−1, T×T_(s)>2R/c+T_(d) may be rewritten as(N_(CS)−1)×T_(s)>2R/c+T_(d). Therefore, N_(CS)>1+(2R/c+T_(d))/T_(s).

Additionally, since N_(pre)=

N_(ZC)/N_(CS)

, N_(pre)<

N_(ZC)+(2R/c+T_(d))/T_(s))

. Thus, N_(pre) may be a function of the cell radius R. Of course, thecell radius may also be varying; and the value of N_(pre) decreases asthe value of N_(CS) increases.

In an embodiment of the disclosure, a limited set of N_(CS) values isconstructed, i.e., for a certain cell radius, the N_(pre) correspondingto the minimum N_(CS) value which is selected from the limited set andis applicable to the cell, is closest to the N_(pre) corresponding tothe minimum N_(CS) value which is selected from the set of all integersand is applicable to the cell. Furthermore, a maximum relativedifference may be constructed from N_(pre). This maximum relativedifference is between the N_(pre)(R), which is determined from theminimum N_(CS) value selected from the set of integers and is applicableto the cell, and the N_(pre)(R), which is determined from the minimumN_(CS) value selected from the limited set and is applicable to thecell. If the finally determined or selected limited set is such a setthat the maximum relative difference between the N_(pre)(R), which isdetermined from the minimum N_(CS) value selected from the set ofintegers and is applicable to the cell, and the N_(pre)(R), which isdetermined from the minimum N_(CS) value selected from the limited setand is applicable to the cell, is minimized in a cell of any radius,this limited set is a required one.

As illustrated in FIG. 2 , curve A indicates that for any one cellradius, an integer from the set of all integers may be selected asN_(CS) of the cell, wherein a maximum number of preamble sequences maybe generated based on the integer selected, and the generated preamblesequences are applicable to the cell. Curve B indicates a set of N_(CS)including a limited number of N_(CS). When the limited number of N_(CS)is applied in cells of all radii, within a certain interval of cellradii, a same N_(CS) will be used for all cell radii. Thus, the N_(CS)should be determined according to the maximum cell radius in theinterval of cell radii. Compared with A, the preamble number generatedaccording to B decreases.

Under these conditions, if the selected limited set ensures that themaximum relative difference between the N_(pre)(R) determined from aN_(CS) value selected from any integer and the N_(pre)(R) determinedfrom a N_(CS) value selected from the limited set is minimized, and itis assumed that the N_(pre)(R) determined from a N_(CS) value selectedfrom any integer is A(R) and the N_(pre)(R) determined from a N_(CS)value selected from the limited set is B(R), and then A(R) and B(R) arerespectively illustrated in FIG. 2 .

As seen from FIG. 2 , there is a small deviation between A(R) and B(R).For a certain cell radius R, the deviation of B(R) from A(R) for somecell radius R may increase the number of required root sequences forthat cell radius R. The increase of the number of root sequences becomesvery important for large cell radii where N_(pre) is small. For example,if A(R)=₃ and B(R)=2, the number of root sequences increasessignificantly, from

64/3

=22 to

64/2

=32. An appropriate measure of the deviation of B from A shouldtherefore weigh the difference A-B with higher weight for small N_(pre),e.g. by considering the maximum relative difference between A(R) andB(R), i.e., [A(R)−B(R)]/A(R). We will adopt the maximum relativedifference between A(R) and B(R) over all cell radii as the measurementof the deviation of B(R) from A(R), and find a set of N_(CS) values thatminimizes this measurement. This set may consist of one N_(CS)=0 and K+1non-zero N_(CS) values. The total number of N_(CS) values in the set isK+2.

For example, in a relatively small cell, it would be possible togenerate 64 ZCZ preambles from a single root sequence if N_(CS)=

N_(ZC)/64

. This value is the smallest value in the set N_(CS)(k).

The maximum value, N_(CS)(K), is the one that allows for having 2 ZCZsequences from a set single root sequence, so it is

N_(ZC)/2

.

For the largest cells there is only one RAP generated from each rootsequence. Therefore, N_(CS)(K+1)=0.

The maximum relative difference between A(R) and B(R), i.e.,[A(R)−B(R)]/A(R), is non-increasing with radius R within the interval of[(r(k−1), r(k)] and the interval being k, as illustrated in FIG. 2 . InFIG. 2 , r(k) denotes the kth cell radius arranged orderly from smallones to large ones. The reason is that B(R) is constant in the interval,whereas A is inversely proportional to the smallest possible N_(CS) forgiven R. This value of N_(CS) increases with the round trip time andhence with R.

If it is assumed that the maximum number of preamble sequences of theset A(R) is N_(pre)(k−1)−1 in the cell radius interval of [(r(k−1),r(k)], the maximum number of preamble sequences of the set B(R)generated in this interval associate with the cell radius r(k), i.e.,the maximum number of preamble sequences is N_(pre)(k). The maximumrelative difference D_(k) in the interval k may be obtained from thefollowing equation:

$D_{k} = \frac{{N_{pre}\left( {k - 1} \right)} - 1 - {N_{pre}(k)}}{{N_{pre}\left( {k - 1} \right)} - 1}$

If D_(k) and N_(pre)(k−1) are given, N_(pre)(k) may be obtained byrearranging the above equation, i.e.:N _(pre)(k)=(1−D _(k))(N _(pre)(k−1)−1)

The maximum relative difference D_(max) for all cell radii may be givenbyD _(max)=max{D _(k)}_(k=1) ^(K).

For N_(pre)(k), we will first allow N_(pre)(k) to be a real number, andthen round the result to the nearest integer. Additionally, N_(pre)(0)and N_(pre)(K) are fixed.

Then D_(max) is minimized if all D_(k) are equal, i.e. D_(k)=D, k=1, 2,. . . , K, as will be proved in the following.

A set of values {N_(pre) ⁽¹⁾(k)}_(k=0) ^(K) is constructed with theconstraint that N_(pre) ⁽¹⁾(k)=N_(pre)(k) for k=0 and k=K, so that D_(k)⁽¹⁾=D, k=1, 2, . . . , K. For this set, D_(max)=D.

Next, another set of values {N_(pre) ⁽²⁾(k)}_(k=0) ^(K) is constructedwith the constraint that for N_(pre) ⁽²⁾(k)=N_(pre) ^((k)) for k=0 andk=K, so that D_(max)<D, i.e. D_(k) ⁽²⁾<D_(k) ⁽¹⁾, k=1, 2, . . . , K.

When k=1, since D_(k) ⁽²⁾<D_(k) ⁽¹⁾ and N_(pre) ⁽²⁾(0)=N_(pre) ⁽¹⁾(0),N_(pre) ⁽²⁾(1)>N_(pre) ⁽¹⁾(1) is obtained according toN_(pre)(k)=(1−D_(k))(N_(pre)(k−1)−1).

When k=2, since D₂ ⁽²⁾<D₂ ⁽¹⁾ and N_(pre) ⁽²⁾(1)>N_(pre) ⁽¹⁾(1), N_(pre)⁽²⁾(2)>N_(pre) ⁽¹⁾(2) is obtained according toN_(pre)(k)=(1−D_(k))(N_(pre)(k−1)−1).

Similarly, for all k, since N_(pre) ⁽²⁾(K)=N_(pre) ⁽¹⁾(K)=N_(pre)(K),N_(pre) ⁽²⁾(k)>N_(pre) ⁽¹⁾(k) is impossible.

Thus, it is impossible to construct a set of values N_(pre) ^((k)) suchthat D_(max)<D, which proves that D_(max) is minimized if all D_(k) areequal, i.e. D_(k)=D, k=1, 2, . . . , K.

In this way, the set of values {N_(pre)(k)}_(k=0) ^(K) which minimizesD_(max) may be found.

Replacing D_(k) by D in N_(pre)(k)=(1−D_(k))(N_(pre)(k−1)−1) andrearranging the equation, a linear difference equation is obtained asfollows:N _(pre)(k)−aN _(pre)(k−1)=−a,wherein a=(1−D).

By recursion, it is obtained from the above equation:

$\begin{matrix}{{N_{pre}(k)} = {{{N_{pre}(0)}a^{k}} + {\frac{a}{1 - a}\left( {a^{k} - 1} \right)}}} & (3)\end{matrix}$

From the above equation and the boundary conditions N_(pre)(0) andN_(pre)(K), a may be determined numerically.

For example, the maximum number of preambles generated from one rootsequence is 64, i.e., N_(pre)(0)=64. The minimum number of preambleobtained by cyclic shift is 2, for example, N_(pre)(14)=2. Thus, a=0.856may be obtained from these two parameters, and all N_(pre)(k), k=1, 2, .. . may further be obtained.

The maximum relative difference is minimized through an approximateminimization by a sub-optimal algorithm, i.e., by minimizing the maximumrelative difference for fictive real-valued maximum number of ZCZ RAPs,and the maximum number of the ZCZ RAPs is thereafter quantized. Themethod is specified below.

By first rounding the fictive real-valued N_(pre)(k) in

${{N_{pre}(k)} = {{{N_{pre}(0)}a^{k}} + {\frac{a}{1 - a}\left( {a^{k} - 1} \right)}}},$the following equation is obtained:N _(CS)(k)=

N _(ZC) /[N _(pre)(0)×a ^(k) +a/(1−a)×(a ^(k)−1)]

(4)

where

x

denotes the maximum integer not greater than x, N_(ZC) is the length ofthe root sequence, N_(pre)(0) denotes the maximum number of preamblesgenerated from the root sequence.

Still taking the above example as an example, if N_(pre)(0)=64 andN_(pre)(14)=2, a=0.856 is obtained based on equation (3). Next, whenN_(ZC)=839, N_(cs)(k), k=0, 1, 2, . . . , 14 obtained based on equation(4) is illustrated in table 1:

TABLE 1 k N_(CS)(k) 0 13 1 15 2 18 3 22 4 26 5 32 6 38 7 46 8 59 9 76 1093 11 119 12 167 13 279 14 419

If only one preamble sequence is obtained for a very large cell, whichis the sequence itself, then N_(CS)=0. Adding this value into the abovetable, table 2 is obtained:

TABLE 2 k N_(CS)(k) 0 13 1 15 2 18 3 22 4 26 5 32 6 38 7 46 8 59 9 76 1093 11 119 12 167 13 279 14 419 15 0

Finally, the true integer value of N_(pre)(k) is obtained fromN_(pre)(k)=

N_(ZC)/N_(CS)(k)

that for some values of k N_(ZC)/N_(CS)(k) are greater than the roundedvalues N_(pre)(k). As illustrated in FIG. 3 , when K=14, the value ofD_(k) obtained from the real number value of N_(pre)(k) is D=0.144. Itcan be seen from FIG. 3 that the true integer values of N_(pre)(k) willcause D_(k) to deviate from D. But the deviation is still very small forall cells except the two largest cells. Thus, the selected limited setof values of N_(CS) is applicable.

It should be noted that if the limited set of values of N_(CS) isdetermined, the limited set of lengths of ZCZ may also be determined,for instance, according to T=N_(CS)−1.

Correspondingly, the disclosure provides an embodiment of an apparatusof determining a set of ZCZ lengths. As illustrated in FIG. 4 , theapparatus includes: a length determination unit 410, configured todetermine a length of a root sequence; and a set selection unit 420,configured to select such a set of ZCZ lengths that, for any cellradius, the maximum number of preambles determined from a ZCZ lengthwhich is selected from the selected set of ZCZ lengths, and isapplicable to the cell and capable of determining a maximum number ofpreambles, is closest to the maximum number of preambles determined froma ZCZ length which is selected from the set of all integers, and isapplicable to the cell and capable of determining a maximum number ofpreambles, wherein the maximum number of preambles is determined by thelength of the root sequence and a ZCZ length selected.

The set selection unit 420 may include: a module 421 adapted for theselection of a set of cyclic shift increments, wherein, the module 421is configured to select such a set of cyclic shift increments that, forany cell radius, the maximum number of preambles determined from acyclic shift increment which is selected from the selected set of cyclicshift increments, and is applicable to the cell, is closest to themaximum number of preambles determined from a cyclic shift incrementwhich is selected from the set of all integers and is applicable to thecell, wherein the maximum number of preambles is determined by the rootsequence length and a cyclic shift increment selected; and a module 422adapted to obtain a set of ZCZ lengths, wherein the module is configuredto obtain the set of ZCZ lengths according to the selected set of cyclicshift increments.

In above apparatus embodiment, the cyclic shift increment selected fromthe selected set of cyclic shift increments is the minimum cyclic shiftincrement in the selected set of cyclic shift increments; and the cyclicshift increment selected from the set of all integers is the minimumcyclic shift increment in the set of all integers.

The disclosure provides an embodiment of a base station, as illustratedin FIG. 4 , which includes: a length determination unit 410, configuredto determine a length of a root sequence; and a set selection unit 420,configured to select such a set of ZCZ lengths that, for any cellradius, the maximum number of preambles determined from a ZCZ lengthwhich is selected from the selected set of ZCZ lengths, and isapplicable to the cell and capable of determining a maximum number ofpreambles, is closest to the maximum number of preambles determined froma ZCZ length which is selected from the set of all integers, and isapplicable to the cell and capable of determining a maximum number ofpreambles, wherein the maximum number of preambles is determined fromthe length of the root sequence and a ZCZ length selected.

The disclosure further provides an embodiment of a mobile communicationsystem, as illustrated in FIG. 5 . The system comprises a base station400 and a mobile terminal 500. The base station 400 is configured tointeract with the mobile terminal 500, and to specify a ZCZ length froma set of ZCZ lengths for the mobile terminal 500; the mobile terminal500 is configured to generate a preamble according to the ZCZ lengthspecified by the base station 400, and to transmit an uplink signal tothe base station 400 using the preamble; the set of ZCZ lengths is sucha set of ZCZ lengths that, for any cell radius, the maximum number ofpreambles determined from a ZCZ length which is selected from theselected set of ZCZ lengths, and is applicable to the cell and capableof determining a maximum number of preambles, is closest to the maximumnumber of preambles determined from a ZCZ length which is selected fromthe set of all integers, and is applicable to the cell and capable ofdetermining a maximum number of preambles, wherein the maximum number ofpreambles is determined from the length of the root sequence and a ZCZlength selected.

In above embodiment of the mobile communication system, the cyclic shiftincrement selected from the selected set of cyclic shift increments isthe minimum cyclic shift increment applicable to the cell in theselected set of cyclic shift increments, the cyclic shift incrementselected from the set of all integers is the minimum cyclic shiftincrement applicable to the cell in the set of all integers.

In general, in embodiments of the disclosure, the selected limited setof N_(CS) values should be such a set that, in a plurality of intervalsof cell radii, the maximum relative difference between the maximumnumber of the ZCZ RAPs determined from the minimum N_(CS) value of thelimited set, which is applicable to the plurality of cells, and themaximum number of the ZCZ RAPs determined from a plurality of N_(CS)values of a set of integers which are applicable to the plurality ofcells is minimized. Furthermore, a limited set of ZCZ lengths may beselected. Of course, in a plurality of intervals of cell radii, themaximum relative difference between the maximum number of the ZCZ RAPsdetermined from the minimum ZCZ length of the limited set of ZCZlengths, which is applicable to the plurality of cells, and the maximumnumber of the ZCZ RAPs determined from a plurality of ZCZ lengths of theset of all integers which are applicable to the plurality of cells isminimized.

What are described above are only preferred embodiments of thedisclosure. It should be noted that, for a person skilled in the art,variations and improvements may be made without deviating from theprinciple of the disclosure. Those variations and improvements are allregarded to be within the scope of the disclosure.

The invention claimed is:
 1. A communication method performed in awireless communication network, comprising: notifying a terminal ofcyclic shift increment N_(CS) configuration information indicating anN_(CS) value, the N_(CS) value belonging to a set of cyclic shiftincrements including following cyclic shift increments: 0, 13, 15, 18,22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; and receiving,from the terminal, a random access preamble corresponding to the N_(CS)value.
 2. The communication method according to claim 1, furthercomprising: determining a time advance in accordance with the randomaccess preamble; and transmitting the time advance to the terminal. 3.The communication method according to claim 1, further comprising:sending a downlink synchronization signal to the terminal for downlinksynchronization with the terminal.
 4. The communication method accordingto claim 1, wherein a cyclic shift increment 0 in the set of cyclicshift increments indicates that one preamble sequence is generated fromone root sequence.
 5. The communication method according to claim 4,wherein the cyclic shift increment 0 in the set of cyclic shiftincrements corresponds to a same cyclic shift as that of a cyclic shiftincrement
 839. 6. An apparatus operable to communicate in a wirelesscommunications network, the apparatus comprising: a processor; and anon-transitory computer readable storage medium storing programming forexecution by the processor coupled to the storage medium, theprogramming including instructions that cause the apparatus to: notify aterminal of a cyclic shift increment N_(CS) configuration informationindicating an N_(CS) value, the N_(CS) value belonging to a set ofcyclic shift increments including following cyclic shift increments: 0,13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167, 279, and 419; andreceive, from the terminal, a random access preamble corresponding tothe N_(CS) value.
 7. The apparatus according to claim 6, wherein theprogramming further includes instructions that cause the apparatus to:determine a time advance in accordance with the random access preamble;and transmit the time advance to the terminal.
 8. The apparatusaccording to claim 6, wherein the programming further includesinstructions that cause the apparatus to: send a downlinksynchronization signal to the terminal for downlink synchronization withthe terminal.
 9. The apparatus according to claim 6, wherein a cyclicshift increment 0 in the set of cyclic shift increments indicates thatone preamble sequence is generated from one root sequence.
 10. Theapparatus according to claim 9, wherein the cyclic shift increment 0 inthe set of cyclic shift increments corresponds to a same cyclic shift asthat of a cyclic shift increment
 839. 11. A communication methodperformed in a wireless communication network, comprising: receiving,from a base station, cyclic shift increment N_(CS) configurationinformation indicating an N_(CS) value, the N_(CS) value belonging to aset of cyclic shift increments including following cyclic shiftincrements: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167,279, and 419; generating a random access preamble based on the N_(CS)value; and sending the random access preamble to the base station. 12.The communication method according to claim 11, further comprising:receiving, from the base station, a time advance that is determined inaccordance with the random access preamble.
 13. The communication methodaccording to claim 11, further comprising: receiving a downlinksynchronization signal from the base station to be synchronized with thebase station in downlink.
 14. The communication method according toclaim 11, wherein a cyclic shift increment 0 in the set of cyclic shiftincrements indicates that one preamble sequence is generated from oneroot sequence.
 15. The communication method according to claim 14,wherein the cyclic shift increment 0 in the set of cyclic shiftincrements corresponds to a same cyclic shift as that of a cyclic shiftincrement
 839. 16. An apparatus operable to communicate in a wirelesscommunications network, the apparatus comprising: a processor; and anon-transitory computer readable storage medium storing programming forexecution by the processor coupled to the storage medium, theprogramming including instructions that cause the apparatus to: receivefrom a base station, cyclic shift increment N_(CS) configurationinformation indicating an N_(CS) value, the N_(CS) value belonging to aset of cyclic shift increments including following cyclic shiftincrements: 0, 13, 15, 18, 22, 26, 32, 38, 46, 59, 76, 93, 119, 167,279, and 419; generate a random access preamble based on the N_(CS)value; and send the random access preamble to the base station.
 17. Theapparatus according to claim 16, wherein the programming furtherincludes instructions that cause the apparatus to: receive, from thebase station, a time advance that is determined in accordance with therandom access preamble.
 18. The apparatus according to claim 16, whereinthe programming further includes instructions that cause the apparatusto: receive a downlink synchronization signal from the base station tobe synchronized with the base station in downlink.
 19. The apparatusaccording to claim 16, wherein a cyclic shift increment 0 in the set ofcyclic shift increments indicates that one preamble sequence isgenerated from one root sequence.
 20. The apparatus according to claim19, wherein the cyclic shift increment 0 in the set of cyclic shiftincrements corresponds to a same cyclic shift as that of a cyclic shiftincrement 839.